Low solar factor (SF) and solar heat gain coefficient (SHGC) values are desired in some applications, particularly in warm weather climates. Solar factor (SF), calculated in accordance with EN standard 410, relates to a ratio between the total energy entering a room or the like through a glazing and the incident solar energy. Thus, it will be appreciated that lower SF values are indicative of good solar protection against undesirable heating of rooms or the like protected by windows/glazings. A low SF value is indicative of a coated article (e.g., IG window unit) that is capable of keeping a room fairly cool in summertime months during hot ambient conditions. Thus, low SF values are sometimes desirable in hot environments. High light-to-solar gain (LSG) values are also desirable. LSG is calculated as Tvis/SHGC. The higher the LSG value, the more visible light that is transmitted and the less amount of heat that is transmitted by the coated article. While low SF and SHGC values, and high LSG values, are sometimes desirable for coated articles such as IG window units and/or monolithic windows, the achievement of such values may come at the expense of sacrificing coloration and/or reflectivity values. In particular, conventional attempts to achieve low SHGC values have often resulted in undesirably low LSG values and/or undesirable visible coloration of the coating. It is often desirable, but difficult, to achieve a combination of acceptable visible transmission (TY or Tvis), desirable glass side reflective coloration (e.g., desirable a* and b* glass side reflective color values), low SHGC, desirably low film side visible reflectance, and high LSG for a coated article in window applications, especially if it desired to use a glass substrate that is not deeply tinted.
SF (G-Factor; EN410-673 2011) and SHGC (NFRC-2001) values are calculated from the full spectrum (Tvis, Rg and Rf) and are typically measured with a spectrophotometer such as a Perkin Elmer 1050. The SF measurements are done on monolithic coated glass, and the calculated values can be applied to monolithic, IG and laminated applications.
It would be desirable according to example embodiments of this invention for a coating to be designed so as to have a combination of acceptable visible transmission (TY or Tvis), low emittance/emissivity, low SHGC, and high LSG for a coated article in window applications.
In certain embodiments of this invention there is provided an insulating glass (IG) widow unit comprising: first and second glass substrates; wherein the first glass substrates supports a low-E coating and a dielectric coating on opposite major surfaces thereof; wherein the low-E coating comprises first, second, and third infrared (IR) reflecting layers comprising silver separated by at least dielectric layers; wherein the dielectric coating comprises a plurality of alternating high index and low index layers that contact each other; and wherein the low-E coating and the dielectric coating are configured so that the IG window unit has an LSG value of at least 2.0, and a ΔC value of no greater than 3.0 as viewed from an exterior of a building in which the IG window unit is to be mounted across a range of angles of at least 85 degrees.